An integrated circuit (hereinafter called IC) card member can be detachably connected to a data processing device such as a printer to function as a part of the device. The data processing device can provide different functions depending on which IC card member is used.
Typically, IC cards such as memory cards comprise mask ROM (Read Only Memory) means or RAM (Random Access Memory) means and are connected to a data processing device by directly connecting the data, address and control lines to corresponding lines of the Central Processing Unit (hereinafter called CPU) of the main device, that is, a control unit 14 as shown in FIG. 1.
When mask-ROM type IC cards are used, it can take a long time (perhaps months) to design, test and implement the mask needed for the expected function. When a RAM type IC card is used there is no such delay, but the card must have therein a battery means in order to prevent loss of stored information when power is turned off. Accordingly, the RAM type card has a disadvantage in price and reliability. An IC card using an electrically erasable-programmable ROM (hereinafter called EPROM) type also has a disadvantage in price.
Problems can arise when the CPU bus of the data processing device is directly connected to that of the IC card member. For example, if the number of connector pins needed to connect the IC card with data processing device increases, the card may be made less convenient and more expensive. Such problems can arise in devices having a 16-bit bus. Further, since the bit-rate of the CPU bus is high, the extension of the CPU bus to the outside of the device increases the risk of errors due to electromagnetic interference. Further, when the IC card is pulled out of the data processing device, there is a risk that the CPU would be adversely affected through the connection to the CPU bus.